A gravity plate was used to simulate a gravity environment on starships. Gravity plating could be lined along a ship's exterior hull, or across the interior deck plates.
Gravity plating could be constructed from Duranium sheeting. (VOY: "Alice")
In 2151, when the Enterprise NX-01 was preparing to engage an unknown enemy vessel, Commander Tucker and Lieutenant Reed intentionally overloaded the phase modulators to increase the yield of Enterprise's phase cannons, using the gravity plating of the affected decks to absorb the recoil. (ENT: "Silent Enemy")
In the mirror universe, in 2155, Captain Archer used the Defiant's gravity plating to increase the gravity under Slar, weighing him down to the ground. (ENT: "In a Mirror, Darkly, Part II")
In 2371, Benjamin Sisko builds gravity plating into his replica Bajoran lightship because historically-accurate weightlessness would make him queasy. (DS9: "Explorers")